This invention relates to gas turbine engines and more particularly to a blade and disk assembly having sideplates in such an engine.
A gas turbine engine has a compression section, a combustion section and a turbine section. A rotor assembly extends axially through the turbine section and the compression section. The rotor assembly includes disks and rows of rotor blades extending outwardly from the disk. A stator circumscribes the rotor. An annular flow path for working medium gases extends axially through the turbine section between the stator assembly and the rotor assembly.
Conventionally, each disk is adapted by a plurality of circumferentially spaced slots to receive the rotor blades. These slots extend in a substantially axial direction across the rim of the disk. The rotor blades generally have an airfoil section, a platform section and a root section. The root section of each rotor blade engages a corresponding slot in the disk. The platform sections of adjacent rotor blades generally abut. In many constructions the platforms are radially spaced from the disk. Because the blades are also circumferentially spaced one from another to engage the circumferentially spaced slots, a gap is left between the blades beneath the abutting platforms. A rotor sideplate is attached to the disk to close the gap. This closure blocks the hot working medium gases from flowing under the platform and causes the working medium to follow the prescribed path along the annular flow path. An example of such a structure is shown in U.S. Pat. No. 3,137,478 to Farrell entitled, "Cover Plate Assembly for Sealing Spaces Between Turbine Buckets".
Fuel is burned in the combustion section with the working medium to add energy to the working medium. The temperature of the working medium increases dramatically and may be as high as 2500.degree. F. or greater immediately downstream of the combustion. The hot working medium flows out of the combustion section and into the turbine section. The rotor blades are bathed in the hot medium and, in many constructions, are cooled by cooling air which flows through the interior of the blade. A cooling air cavity between the bottom of the blade root and the disk provides a manifold for the cooling air passing from the disk into the turbine blade. The ends of such a cavity are also sealed by sideplates in these constructions. The sideplates may also provide axial retention of the rotor blade by engaging the disk. An example of such a construction is shown in U.S. Pat. No. 3,728,042 to Hugoson et al. entitled, "Axial Positioner and Seal for Cooled Rotor Blade".
Many constructions use a single sideplate to cover the gap between adjacent blade roots and the ends of the cooling cavity. An example of such a construction is shown in U.S. Pat. No. 3,936,222 to Asplund et al. entitled, "Gas Turbine Construction". Such sideplates are retained axially and radially as a unit. Because the entire rotational load of the sideplate is carried by a shoulder on the disk, the sideplate is thickened to decrease the total stresses near the single point of attachment. This thickness enables a satisfactory fatigue life by keeping the total stress below the fatigue strength. As gas turbine engines are operated at higher and higher speeds, thickening the sideplate does not always result in an acceptable fatigue life. In addition, increasing the thickness adds weight and axially displaces the center of gravity of the sideplate in the downstream direction. Accordingly, increasing the thickness increases the bending stresses which the sideplate exerts on the disk and adversely affects the fatigue life of the disk.
Scientists and engineers are searching for a sideplate which provides axial retention to a rotor blade and blocks the passage of working medium between the roots of adjacent rotor blades while sealing the cooling air cavity between the blade root and the disk. The weight of the sideplate must be low and the total stresses in such a sideplate must be below the fatigue strength of the sideplate.